In general, vehicle drivelines transmit torque from a vehicle's engine to its wheels. Automotive drivelines sometimes include power transfer units (PTUs, also known as power take-off units) for selectively distributing torque among shafts in the drivelines. A PTU typically consists of a housing that encloses and supports gears, shafts, and bearings. Two shafts of the PTU may need to be coupled together and the relative axial movement of the shafts constrained by a coupler. Packaging in automotive drivelines, as elsewhere in automobiles, often demands inflexible size constraints which can frustrate or prevent installation of the shafts and any coupler on the shafts, or require a coupler of a size and shape that may be damaged (e.g. plastically deformed or broken) during installation.